Chy102-Lecture 04 - Dr. Raafat Aly 4 th lecture General...

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Unformatted text preview: Dr. Raafat Aly 4 th lecture General Chemistry Chem102 for Engineering 14/11/2007 D o n e 2 Objectives Types of chemical reactions occurring in aqueous solutions Precipitation reactions Acid-base reactions Reduction-oxidation reactions 3 I- Precipitation reactions When two solutions are mixed, an insoluble substance sometimes forms ; that is, a solid forms and separates from solution. Such a reaction is called a precipitation reaction precipitation reaction , and the solid formed is called a precipitate precipitate . Example: AgNO 3 (aq) + Na 2 CrO 4 (aq) products Ag + (aq) + NO 3- (aq) + 2Na + (aq) + CrO 4 2- (aq) orange precipitate Predicting whether a precipitation reaction will occur or not 1. Note the ions present in the reactants (Ag + , NO 3- , Na + , and CrO 4 2- ). 2. Consider the possible cationanion combinations (in addition to the original reactants AgNO 3 and Na 2 CrO 4 which are soluble, the other possibilities are NaNO 3 and Ag 2 CrO 4 . 3. Decide whether any of these combinations are insoluble (consult the following table). Types of Chemical Reactions Solvated or hydrated ions 4 Solubility Rules for Ionic Compounds in Water 1. Most nitrate salts are soluble . 2. Most salts containing the alkali metal ions (Li + , Na + , K + , Cs + , Rb + ) and the ammonium ion (NH 4 + ) are soluble . 3. Most chloride , bromide, and iodide salts are soluble except salts containing the ions Ag , Pb , and Hg . In our example, which one of these two salts NaNO 3 or Ag 2 CrO 4 is the precipitate? According to rule no. 1, NaNO 3 are soluble 2 4 5 Molecular equation Shows all substances intact (undissociated compounds) Total ionic equation Shows all soluble substances as separate, solvated ions. Ag 2 CrO 4 (s) is the only undissociated substance The net ionic equation Eliminates the spectator ions , which are not really involved in reaction, and shows only the reacting species 6 The driving force for precipitation reaction The event that causes the reaction to occur is the removal of ions from solution to form the slightly soluble precipitate ....
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Chy102-Lecture 04 - Dr. Raafat Aly 4 th lecture General...

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